BACKGROUND: Current methods of improving medication adherence for health problems are mostly complex, labour-intensive, and not reliably effective. Medication 'reminder packaging' which incorporates a date or time for a medication to be taken in the packaging, can act as a reminder system to improve adherence. OBJECTIVES: The objective of this review was to determine the effects of reminder packaging to enhance patient adherence with self-administered medications taken for one month or more. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) and the Database of Abstracts of Reviews of Effects (DARE) (The Cochrane Library Issue 3, 2004), MEDLINE, EMBASE, CINAHL and PsycINFO from the start of the databases to 1 September 2004. We also searched the internet, contacted packaging manufacturers, and checked abstracts from the Pharm-line database and reference lists from relevant articles. We did not apply any language restrictions. SELECTION CRITERIA: We selected randomised controlled trials with at least 80% follow up, comparing a reminder packaging device with no device in participants taking self-administered medications for a minimum of one month. DATA COLLECTION AND ANALYSIS: Two reviewers independently assessed studies for inclusion, assessed quality, and extracted data from included studies. Where considered appropriate, data were combined for meta-analysis, or were reported and discussed in a narrative. MAIN RESULTS: Eight studies containing data on 1,137 participants were included. Six intervention groups in four trials provided data on the percentage of pills taken. Reminder packaging showed a significant increase in the percentage of pills taken, weighted mean difference 11% (95% confidence interval (CI) 6% to 17%). Notable heterogeneity occurred among these trials I(2 )= 96.3%. Two trials provided data for the proportion of self-reported adherent patients, reporting a reduction in the intervention group which was not statistically significant, odds ratio = 0.89 (95% CI 0.56 to 1.40). No appropriate data were available for meta-analysis of different clinical outcomes, the most common of these being blood pressure (three out of eight trials). Other clinical outcomes reported were glycated haemoglobin, serum Vitamin C and E levels, and self-reported psychological symptoms (one trial each). AUTHORS' CONCLUSIONS: Reminder packing may represent a simple method for improving adherence for patients with selected conditions examined to date. Further research is warranted to improve the design and targeting of these devices.